1. Field of Invention
The present invention relates to a composite exterior door structure which comprises an inner frame of structural members formed of synthetic low thermally conductive material and wherein the door has an outer door covering of metallic material which is secured to permit expansion and contraction thereof independently of the structural members, and further wherein an inner door covering in immovably secured to the structural members and is thermally insulated from the outer door covering.
2. Description of Prior Art
There exists various types of exterior doors for use primarily in residential structures. In the past twenty years the construction of such doors has greatly evolved from the traditional wooden door to composite door structures. The reason for this change is that the traditional wooden door was found to have important disadvantages, and namely that it requires considerable maintenance and provides poor insulation. It is also relatively expensive to fabricate and maintain large inventories of these wooden doors or other type doors to satisfy the consumer demand. A further disadvantage of such exterior doors is that they often require the installation of a storm door in front of them to provide better insulation and to protect the door from the effects of inclement weather.
Composite wooden door structures are know and some are constructed with pressed polyurethane panels secured to a wooden frame. However, like the wooden door these are still subject to warping as the wood absorbs humidity, and the doors still require maintenance, such as repainting. Likewise, laminated wood doors are subjected to the same disadvantage even if the core of the door is formed of polyurethane. A further disadvantage with these laminated doors is that there is a limit as to how much window space can be provided in the door.
Another type of exterior door which has become popular is the steel door insulated with an inner polyurethane core. However, with these doors very few models are offered because of the cost of the molds which shape the metal sheet to simulate door stiles and panels. It is also required to maintain a large inventory of these doors to offer the existing designs in various standard door dimensions. The stocking of these doors is expensive. These known steel doors are also subjected to distortion due to expansion and contraction of the metal caused by the change in temperature, and this causes the door structure to warp further causing secondary problems, such as poor insulation with the door frame. The aesthetics of many of these steel doors is limited due to the cost of providing a large inventory of motifs. Also, screw heads which secure the weather sealing door bottom to the interior of the door frame are usually apparent from the outer face of the steel covering and this degrades the quality of the door. However, these doors generally offer good insulation with the exception of those that have motifs pressed therein making portions of the door very thin. Metal doors are usually constructed with inner and outer metal surfaces connected to an inner core, and the spaces therebetween are filled with an insulating foam, such as polyurethane. A further disadvantage of such doors is that the interior surface covering of the door is also metal and this reflects a "cold" feeling to the interior surface and surrounding space.
Fiber doors are also known, and these are also insulated with a polyurethane inner core and they have generally the same disadvantages as the steel doors, although they provide better peripheral insulation and are less subjected to warping as they do not absorb humidity as with steel doors having wooden inner frames, but still most of the models maintain the use of wooden frames.
Finally, some European products do approach the type of construction disclosed herein, but are not of the composite type, as they usually are constructed of a thermally broken aluminum or PVC tubular perimeter with "glazed in" insulated panels or glass units. The perimeter tube, because of its construction, is not filled with insulation as the present invention.